Hawai‘i State Department of Health – Safe Drinking Water Branch
06/01/2018 – 09/31/2019
The Hawai‘i State Legislature passed Act 125 in 2017 that mandated all cesspools in the state be replaced by 2050. There are over 80,000 cesspools in the state and cost estimates range from $20,000 to $80,000 for each septic system and/or aerobic treatment unit (ATU), In addition, some locations will necessitate advanced treatment to include nitrogen removal, filtration, and disinfection, which will increase capital and on-going operation and maintenance (O&M) costs as well as regulatory costs to manage all of these new systems to ensure they function as intended. This project includes modeling of the transport of nitrate from cesspools to groundwater and the ocean, cost/benefit analyses of upgrades to onsite sewage disposal systems (OSDS), maintaining the drinking water supply by limiting nitrogen leaching from cesspools and other sources, and to improve nearshore water quality. The decision analysis modeling considers the consequences of the alternatives using values such as preference scales, objective weights, and risk attitudes; and uses models to determine a ranking of the optimum alternatives to achieve the stated objective(s) which can include least cost or best water quality or a combination of objectives. In such an analysis, the costs are for the cesspool upgrades and capital, O&M, and management are considered objective weights.